Montshire Minute: New Planets

Originally aired during the week of May 10, 1999

Monday

A few weeks ago astronomers reported a discovery: they found three planets circling around a star a scant 44 million light years from earth (one light year is, oh, about 6 trillion miles away. Not easy commuting distance). In any case, what's the big deal with this? Well, the big deal is: WE'VE NEVER FOUND ANOTHER PLANETARY SYSTEM BEFORE! In recent years, astronomers have found several stars with single planets, but never as many as three. The trio of planets, scientists think, really don't resemble our solar system. At least two of them are at least twice as big as Jupiter, and one is much closer to its sun than Mercury is to our sun! Nonetheless, it indicates there may be many other solar systems out there, not just stars with individual oddball planets circling around them.

Tuesday

In Copernicus' time, it was believed that the sun, moon and stars circling in the heavens above were like a big planetarium show for the enjoyment of skywatchers. In other words, the earth was thought to be fixed at the center of the universe, and all the planetary bodies moved around it. Then Copernicus came along and upset the apple cart. He dredged up an idea proposed by several Greek astronomers that the earth and other planets have a circular orbit around the sun. It was left to later astronomers like Johann Kepler and Sir Isaac Newton to explain the more elliptical paths of orbiting planets. But the idea that the earth was no longer the center of the universe - woah! - that was pretty radical. The earth, we now realize, is just one of perhaps countless planets circling around other stars in other corners of the universe.

Wednesday

In light of a recent discovery of another entire solar system several weeks ago, we're been talking about our own solar system and what makes it tick. What keeps the planets in constant orbit around the sun? The key word is: gravity. The gravitational force exerted by the sun is strong enough to hold nine planets in its sway, from Mercury (58 million kilometers from the sun) to Pluto (about 6 billion miles away). Gravity is a force that happens between any two objects, and its intensity depends on the relative size of the objects and the distance between them. If the earth were twice as far from the sun as it is now, the sun's gravitational pull on us would only be a quarter of what it is now. Planets also exert a gravitational pull on each other, but size matters. The sun is by far the biggest thing in the solar system, and keeps everything circling around it.

Thursday

Scientists and philosophers alike have long predicted that our solar system was not unique: that somewhere out there, other planets were circling other suns. Since Pluto was discovered in 1930, no planet circling a sun-like star had ever been found. Then, beginning in October of 1995, astronomers began finding planets orbiting distant stars. A few weeks ago, two teams of researchers announced the discovery of an entire solar system, located a mere 44 million light years away. Many of these new planets appear to be huge gas giants, bigger than our biggest (Jupiter), and circling very close to their suns in dramatic elliptical orbits. Researchers cannot actually see these new planets with telescopes. They can only detect, by a regular change in the wavelengths of a star's light, that some enormous object - at a particular distance, and of a particular mass - is orbiting that star.

Friday

Early astronomers like Kepler and Galileo knew that the earth and other planets orbited the sun. It was left to Sir Isaac Newton to explain what caused this motion. Newton's law of universal gravity does the job pretty well. Gravity, he explained, is the attraction of every bit of matter to another bit. The bigger an object it is, the more gravitational force it has. So in addition to the Sun's pull on all the planets, the planets tug on each other a little bit. By using Newton's Laws, astronomers have been able to predict the presence of planets before they've actually seen them. For instance, careful studies by a French astronomer named Laverrier showed that planet Uranus' orbit was slightly irregular. He concluded that Uranus was being attracted by another unseen planet, and calculated its position in the sky using Newton's Law of universal gravitation. In 1846, a German astronomer found the planet Neptune exactly where Laverrier said it should be.